Abstract
With today 's virtual reality systems, it is difficult to directly and precisely create and modify complex objects in a virtual reality environment. One of the most important reasons is the absence of a suitable model representation that can efficiently support solid modelling in a virtual reality environment. A hierarchically structured constraint-based data model for solid modelling in the virtual reality environment is presented in this paper. The data model integrates a high-level constraint-based model for precise object definition, a mid-level CSG/Brep hybrid solid model for supporting hierarchical geometry abstractions and object creation, and a low-level polygon model for real-time visualization and interaction in the virtual reality environment. Constraints are embedded in the solid model and are organized at different levels to reflect the process of solid modelling. This data model not only provides precise object definition, but also supports real-time visualization and interaction in the virtual reality environment.